Packaging machines for the wrapping of packing pieces with plastic film are often used for the packing of newspapers and magazines. The newspapers and magazines are typically guided through the transport channel by means of the transport device in packs of different heights or as a single copy. The newspapers and magazines are wrapped in the machine by plastic film.
The plastic film is generally pulled from two rolls, one of which is arranged below the transport device, and the other one above. The plastic films are welded or connected approximately at the height of the transport device. As a result, the plastic films form a closed web or film wall running transversely to the transport direction of the packing pieces (e.g., newspapers and magazines). The plastic film from the lower roll applies itself from below and between the transport device as the packing pieces move against the plastic film from the lower roll. The upper roller guides the plastic film to be deposited around the front face and the upper side of the packing pieces. The wrapped packing pieces are then guided to the transport device with the help of the film cutting and welding or connecting unit descending from above in the direction of the transport band. The plastic film from the upper roller is welded or connected to the plastic film from the lower roller by two parallel weld seams and the plastic films are then cut between the two weld seams. The packing piece which is wrapped in such a manner with a circulating film tube at its front and back face, and its upper and lower side, is subsequently ejected by the transport device.
During the packing process, it is particularly important when wrapping flexible packing pieces (e.g., single newspapers, magazines etc.) that the film piece supplied from above is wrapped around the packing piece essentially without any tension. If the-plastic film is wrapped with tension around a flexible packing piece, the flexible packing piece can be damaged by the tension force in the plastic. For instance, a single newspaper will be bent or partially rolled up during the wrapping process. Prior art wrapping systems that pull plastic film off a roll of film do not do not allow a tension-relieved wrapping of the packing piece, thus result in damage to the flexible packing piece.
Some prior art packing systems have incorporated a buffer device to address the damage issue to flexible packing pieces. These prior art buffer devices consist of elaborate mechanical arrangements that incorporate the use of a plurality of deflection rollers, of which one or more of the rollers are arranged to be moveable in such a manner that their center distance can freely adjust to the fixed rollers. Even with such a prior art buffer device, the weight and inertia forces of the deflection rollers have to be overcome during the pulling of the plastic film. As a result, the plastic film is not wrapped around the flexible packing piece in a tension-free manner. When using these prior art buffer arrangements, it has been found that the plastic film tends to charge itself statically as the plastic film passes over the plurality of deflection around rollers. The statically charged plastic film has a tendency to adhere to neighboring surfaces, whereby the adhesion forces arising from the static charge can be considerable and can even lead to stretching of the plastic film. The same phenomenon was found to occur when the film buffer was formed as a film tray made of a tin box or the like, into which the plastic film was deposited after being pulled off from the roll of plastic film.
In view of the present state of technology which respect to wrapping machines, there is a demand for a plastic wrapping machine that reliably and efficiently wraps packing pieces and reduces or prevents damage to flexible packing pieces during the wrapping process and reduces the build-up of a static charge on the plastic film.